We have pursued several questions using recombinant DNA techniques. (1) the transfection procedure, including preparation of competent E. Coli and transfection with plasmid, has been optimized using bacterial strain MC1061 and plasmid pBR322 with and without inserts. (2) Gamma-phage containing the gene(s) for pro-opiomelanocortin (POMC) have been isolated from a Xenopus genomic library using the pBR322-derived recombinant plasmid pKSU16, which contains cDNA for mouse POMC mRNA. (3) The mouse POMC insert is being used to screen colonies containing plasmids with expressed sequences of Xenopus anterior pituitary. (4) A complete library of expressed sequences in adult mouse brain is being developed. (5) Work on cloning of differentiation-specific sequences of mouse neuroblastoma cells continues.